First, start working the hours that they actually pay you for.

Take a personal day.

Understand that you have a business relationship with your employer. Mentally, you have to be ready to tell your employer that "I'm sorry, but I'm really not in a position to subsidize your business any further."

If you haven't already, contact the colleagues that left and connect with them (add them to linked-in, etc). Ask them if you can use them as a reference, see if they have any job leads. Get the contacts of the people you still work with - before they leave.

Do not waste energy trying to fix the company you work for. You just can't. Yes it sucks but that is reality.